ECU choice for ‘95 Honda Civic

[ttrainxl]

I have a stock ‘95 Civic Ex with the D16z6 and a 5 speed transmission. I’ve been getting anywhere between 39-44 mpg, depending on the temperature outside. I just bought a D15z1 long block from the junkyard. (For the non Honda guys, this is from the Civic Vx.)

My plan is to put the D15z1 head on the D16z6 block. I don’t want to swap the entire engine in for now. Swapping the head will bump compression up to 10.7:1 with a thicker head gasket. I’d like to make about 100-110 hp with this setup, rather than the miserable 90hp stock D15z1 engine provides. I don’t have the P07 ECU yet and I’m wondering if a chipped P28 with P07 fuel maps would give me more tuning ability. I know almost nothing about tuning but I’m curious if a chipped P28 and possibly Hondata will open up a little more power and fuel economy that a stock P07 ECU would give me. It seems that if you can tune an engine for more power, you should be able to tune for more fuel efficiency as well.

Anyone have thoughts on this? I’m aware of the five wire O2 sensor issue and I’m aware that my engine will be running in Vtec at 70mph and that I need to swap a transmission, or preferably (after looking at D series transmission gear ratios), keep my transmission and swap in a lower final drive. Right now I’m only asking about the ECU options.

Any help is much appreciated. Thanks.

[Ecky]

Originally Posted by ttrainxl

I have a stock ‘95 Civic Ex with the D16z6 and a 5 speed transmission. I’ve been getting anywhere between 39-44 mpg, depending on the temperature outside. I just bought a D15z1 long block from the junkyard. (For the non Honda guys, this is from the Civic Vx.)

My plan is to put the D15z1 head on the D16z6 block. I don’t want to swap the entire engine in for now. Swapping the head will bump compression up to 10.7:1 with a thicker head gasket. I’d like to make about 100-110 hp with this setup, rather than the miserable 90hp stock D15z1 engine provides. I don’t have the P07 ECU yet and I’m wondering if a chipped P28 with P07 fuel maps would give me more tuning ability. I know almost nothing about tuning but I’m curious if a chipped P28 and possibly Hondata will open up a little more power and fuel economy that a stock P07 ECU would give me. It seems that if you can tune an engine for more power, you should be able to tune for more fuel efficiency as well.

Anyone have thoughts on this? I’m aware of the five wire O2 sensor issue and I’m aware that my engine will be running in Vtec at 70mph and that I need to swap a transmission, or preferably (after looking at D series transmission gear ratios), keep my transmission and swap in a lower final drive. Right now I’m only asking about the ECU options.

Any help is much appreciated. Thanks.

Hondata allows you to change the VTEC crossover point, write your own fuel and spark tables, and adjust fuel enrichment (among many, many other things).

What Hondata doesn't do is factory lean burn. You can't (to my knowledge) chip any of the factory lean burn ECUs. The VX/HX ECU have separate tables that are used during lean burn operation, and trying to tune a P28 to do something similar has some compromises you might find unacceptable, particularly during warmup. Additionally, if you intend to run P07-style fuel maps, you'll also need the P07 spark tables, and I am not sure if anyone has them. That said, I had a lot of fun playing with my Hondata setup (see my K24 swapped Insight thread for details).

What might actually work best, is using a P07 ECU as-is, and having the injectors modified for ~7-10% more fuel flow. The spark tables will be a bit off due to the higher compression, but not by much, and you can probably drive around as-is by running 89 rather than 87 and pulling 1-3 degrees of ignition timing at the distributor (which is approximately what you'd want for the extra compression anyway).

Alternately, you could do an OBDII conversion and run an HX (P2M?) ECU, again pulling just a bit of ignition advance, and with higher octane fuel to take care of knock.

[ttrainxl]

Good info. Thank you. Does the old APEXi VAFC control VTEC crossover? I used to have one of those about 20 years ago that I wanted to use in my GSR and I never installed it. I wonder if I could bump VTEC crossover up to maybe 3000 rpm (think P07 has it cross at 2500) and not swap out the final drive or a whole transmission.

I guess sticking with a stock P07 ECU is probably the easiest way to go.

[Ecky]

Originally Posted by ttrainxl

Good info. Thank you. Does the old APEXi VAFC control VTEC crossover? I used to have one of those about 20 years ago that I wanted to use in my GSR and I never installed it. I wonder if I could bump VTEC crossover up to maybe 3000 rpm (think P07 has it cross at 2500) and not swap out the final drive or a whole transmission.

I guess sticking with a stock P07 ECU is probably the easiest way to go.

Never used one, but I assume it would work. It's worth noting, the crossover point is not just RPM dependent, but also load dependent - at part throttle it'll cross over higher. For the best powerband you'd want to set VTEC crossover to whatever point makes it imperceptible, but setting it higher (where you get a noticeable increase in power) would probably make cruising more frugal, as you'd be valve-limiting the air into the motor and cutting pumping losses. I doubt the difference would be large though. I wonder if the P07 allows lean burn after VTEC?

Low hanging fruit with economy will be with a taller FD, from my experience. Going from a ~4.4 to a ~3.4 FD in my Insight build was worth something like 6-8mpg while cruising.

Regardless, the challenge after a head swap will be to get knock under control. Whatever you do, you'll need to get fueling somewhat close, and you'll need to pull a couple degrees of timing, and likely up your octane.

[ttrainxl]

Yeah I’ve already resigned myself to using 93 octane after this. (In Virginia, our pumps have 87, 89, and 93. You can also get 89 or 90 non ethanol in many places.). I know some places have 91 octane premium.

The combustion chamber volume in a P07 head is a tiny 25.x cc, compared to 34ish for other heads. There are a couple head gasket choices, and the thickest one brings compression from the stock 9.2 up to 10.73:1 I think. The thinner one is closer to 11:1. Pretty standard for higher performance honda engines in stock form, so I’m not too worried about it, but I don’t plan on using 87 octane anymore.

My stock transmission has final drive of 4.25, but the D15z1 transmission (forget the code now) is more like 3.4. One of the other trim levels has something like 3.77, which I think would put my engine speed in an acceptable range at 70mph. Right now I’m at about 2500 at 70mph, which is the crossover point for Vtec in the D15z1. I didn’t realize it was dependent on load though. I remember having a 98 civic ex and on the highway (cruising faster than I should have, but I was young), vtec crossed over when I accidentally sped up by only a couple mph. I could feel it and hear it and all of a sudden I was going about 98mph. So I do think it will cross over even if cruising at a reasonable speed if I don’t do something about it. I’m hoping a 3.77 fd will keep the car somewhat drivable and allow me to cruise up to maybe 76-78mph before vtec crosses. I try to stay around 70-75 on our 70mph highways. 80+mph is a wreckless driving ticket in VA. I had a stock VX once and I thought it was virtually undriveable. It made no power and the gearing just sucked. But I was 21 and only had it because my GSR had just been stolen, so going from the GSR to the VX was quite a difference. That was a long time ago and I’m looking for something different now, but I still want the car to be somewhat fun to drive.

[Ecky]

Getting a bit off topic, but I'm rather surprised people don't complain about the gearing in my current MX-5. I've heard some people just drive around in 5th or even 4th gear on the highway. I guess they don't like shifting. The final drive (rear ratio) is 2.86, and it's a 1.5L. It's rare I encounter a car where I wouldn't choose taller gearing.

[ttrainxl]

Wow, that’s super low. I just looked at D series ratios again and the VX has a 3.25 final drive compared to my 4.25. The 96-00 DX, LX, HX, and CX all use a 3.722 final drive. I think that’s a good compromise and the rest of my transmission has better ratios for 2nd, 3rd, and 4th. 1st and 5th are the same for most D series.